Emergency breathing apparatus are used in situations where fire, smoke, dust and debris, or other impediments prevent normal breathing during a rescue. These breathing apparatus provide oxygen to the user and prevent smoke or other pollutants from entering the device. For safety reasons, many of these devices also include two-way communication devices to assist in rescue or coordination of efforts to fight a fire, etc. Two way communication devices typically comprise microphones powered by direct current batteries, where the voltage is used to amplify a voice for transmission via a transceiver to a remote receiver. An issue that plagues communication in emergency situations is that the microphone picks up and amplifies the heavy breathing and pronounced movement of air, leading to a transmission that is difficult to interpret and makes critical communication challenging.
FIG. 1 depicts a prior art two wire system for communicating audio signals. In this circuit, a first wire carries both the audio signal and a direct current. A second wire is provided that serves as a ground/return path. The problem with this circuit is that it is impossible to isolate the audio signal and filter it effectively without interrupting the power signal. This results in a noisy audio signal that has poor quality and can lead to dangerous repercussions when communication is critical in an emergency situation. As constructed, the microphone tends to be very sensitive and picks up every minute sound while active. During normal modes of oxygen mask operation, the microphone is active when the wearer is not inhaling (and thus active for speaking) and not active when the wearer inhales. However, during certain modes of oxygen mask operation the microphone is continually active, and the continuous sounds of air rushing over the microphone are captured. This continuous unwanted “noise” is obtrusive and severally impedes effective communication.